1. Field of the Invention
This invention relates generally to the field of elevator control systems and more particularly to such control systems employing elevator security and safety devices.
2. Description of the Related Art Including Information Disclosed Under 37 C.F.R. .sctn.1.97-1.99
In known elevator systems, an elevator car arrives at a floor and the hoistway doors and the elevator car doors at that floor open together to provide access in and out of the car. Subsequently, the elevator car doors close and the car automatically proceeds to its next destination. If a hoistway door on any floor is maliciously or accidentally opened when the elevator car is not present at that floor, the elevator car in the shaft in which the hoisting door was forced open is brought to a halt in known elevator systems. Disadvantageously, this allows a criminal, juvenile or any other unauthorized personnel to open a set of hoistway doors at the floor above the car, resulting in the car stopping by such opening thereby enabling such unauthorized individuals to gain access to the top of the elevator car. Once the opened spring loaded hoistway doors are released by the unauthorized person, they automatically close and the car in the shaft resumes operation. This allows the individual riding on top of the car to gain access to the inside of the car through the top hatch. Moveover, the individual can ride the elevator car from the outside and jump to adjacent cars moving within the elevator bank. The riding of cars from the outside is informally referred to as "elevator surfing" which is an extremely dangerous and problematic situation occurring in residential urban high rise buildings and college dormitories.
Attempts have been made to provide safety and security devices in elevator systems. In U.S. Pat. No. 5,025,895 to Leone et al. an elevator control system utilizes a proximity detection circuit to discover the presence of a person or an object on the shaft-ride roof of an elevator cab. The proximity detection circuit uses an optical beam source for generating a detection beam across a predetermined area on the elevator roof. In response to the optical beam detecting an unauthorized entry onto an elevator roof, an audible siren is actuated and the operation of the car is discontinued. Unfortunately, unauthorized individuals are able to avoid detection by merely stepping away from the path of the optical beam. Furthermore, the Leone et al. system requires that the car be equipped with costly photoelectric cells and the associated complex circuitry. Moreover, once the individual exits the path of the optical beam, thereby reinstating the beam, the elevator car continues to move from floor to floor at its normal operation. Thus, the unauthorized person is able to ride or "surf" on the top of the moving elevator car once the individual leaves the path of the optical beam. The system of Leone et al. merely detects intrusions in the path of an optical beam and does not address the dangers associated with "elevator surfing."
In U.S. Pat. No. 4,108,281 to Glaser an elevator door protection system prevents a car from moving from a floor when certain switch contacts operated or shunted by unauthorized persons or by a short circuit, an alarm sounds if a cab or hoistway door is opened improperly. The elevator door protection system functions if a first set of switches is operated prior to a second set of designated switches. The operating or shunting of the switches in their procedural order indicates that the switches have been tampered with and a control circuit prevents movement of the car. Disadvantageously, movement of the elevator car is prevented only if the car door switches have been manipulated. Thus, if a hoistway door is opened and subsequently closed on a floor other than the floor at which the car is located without any tampering to the switches, the car will resume its operation. The system of Glaser merely monitors the elevator car doors and does not monitor the opening and closing of hoistway doors located at different floors of a building. Therefore, unauthorized individuals can gain access to the elevator car roof and "ride" on top of the car as it moves through the hoistway or elevator shaft area.
In U.S. Pat. No. 4,367,810 to Doane et al. an elevator control system monitors cab and hoistway doors to arrest motion of the cab if any of the cab or hoistway doors are not closed. The control system employs a microprocessor based cab controller mounted directly on the cab to monitor and analyze the functions operating within the cab. The controller further determines if the car is at a proper distance from a landing or if a car is travelling at an improper speed with respect to a landing. The cab controller communicates with remotely controlled circuits to disable the car motion and a car controller in a machine room inhibits door motion. However, the cab controller of the Doane et al. patent does not function to arrest car motion if unauthorized access to the top of the car is accomplished.